Electromagnetic alignment and scanning apparatus

ABSTRACT

An exposure apparatus that irradiates an energy beam to a substrate includes a projection optical system that projects the energy beam to the substrate, and a support device having a flexible structure to support the projection optical system. According to one embodiment, the flexible structure includes three flexible rods that support the projection optical system from an upper side of the projection optical system. According to an embodiment, extended lines of the respective rods cross at a reference point of the projection optical system.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a movable stage apparatus capable ofprecise movement, and particularly relates to a stage apparatus movablein one linear direction capable of high accuracy positioning and highspeed movement, which can be especially favorably utilized in amicrolithographic system. This invention also relates to an exposureapparatus that is used for the transfer of a mask pattern onto aphotosensitive substrate during a lithographic process to manufacture,for example, a semiconductor element, a liquid crystal display element,a thin film magnetic head, or the like.

2. Description of Related Art

When a semiconductor element or the like is manufactured, a projectionexposure apparatus is used that transfers an image of a pattern of areticle, used as a mask, onto each shooting area on a wafer (or a glassplate or the like) on which a resist is coated, used as a substrate,through a projection optical system. Conventionally, as a projectionexposure apparatus, a step-and-repeat type (batch exposure type)projection exposure apparatus (stepper) has been widely used. However, ascanning exposure type projection exposure apparatus (a scanning typeexposure apparatus), such as a step-and-scan type, which performs anexposure as a reticle and a wafer are synchronously scanned with respectto a projection optical system, has attracted attention.

In a conventional exposure apparatus, a reticle stage, which supportsand carries the reticle, which is the original pattern, and the wafer towhich the pattern is to be transferred, and the driving part of thewafer stage are fixed to a structural body that supports a projectionoptical system. The vicinity of the center of gravity of the projectionoptical system is also fixed to the structural body. Additionally, inorder to position a wafer stage with high accuracy, the position of thewafer stage is measured by a laser interferometer, and a moving mirrorfor the laser interferometer is fixed to the wafer stage.

Furthermore, in order to carry a wafer to a wafer holder on the waferstage, a wafer carrier arm that takes out a wafer from a wafer cassetteand carries it to the wafer holder, and a wafer carrier arm that carriesthe wafer from the wafer holder to the wafer cassette, are independentlyprovided. When the wafer is carried in, the wafer that has been carriedby the wafer carrier arm is temporarily fixed to and supported by aspecial support member that can be freely raised and lowered and that isprovided on the wafer holder. Thereafter, the carrier arm is withdrawn,the support member is lowered, and the wafer is disposed on the waferholder. After this, the wafer is vacuum absorbed to the top of the waferholder. When the wafer is carried out from the exposure device, theopposite operation is performed.

As described above, in the conventional exposure apparatus, the drivingpart of the wafer stage or the like and the projection optical systemare fixed to the same structural body. Thus, the vibration generated bythe driving reaction of the stage is transmitted to the structural body,and the vibration is also transmitted to the projection optical system.Furthermore, all the mechanical structures were mechanically resonate toa vibration of a predetermined frequency, so there are disadvantagessuch that deformation of the structural body and the resonancephenomenon occurred, and position shifting of a transfer pattern imageand deterioration of contrast occurred when this type of vibration istransmitted to the structural body.

Furthermore, because the wafer stage moves over a long distance from thecarrier arm for carrying in and out of the wafer to the exposureposition, it is necessary to provide an extremely long moving mirror forthe laser interferometer. Because of this, the weight of the wafer stagebecomes relatively heavy and the driving reaction becomes large becausea heavy motor with a large driving force is needed. Furthermore, inorder to improve throughput, when the moving speed and acceleration ofthe stage needs to be increased, the driving reaction becomes evenlarger. In addition, as the weight and acceleration of the stageincrease, the heating amount of the motor increases, and there is adisadvantage such that measurement stability or the like of the laserinterferometer deteriorates.

Furthermore, in the case of carrying the wafer into and out of theexposure apparatus, the wafer is temporarily fixed and supported on thetop of a special support member, so carrying in and out of the waferconsumes time. This causes deterioration of throughput. Additionally, asone example, because giving and receiving of the wafer is performedbetween the carrier arms, the probability of the wafer beingcontaminated is high, and the probability of having an operation errorwhen the wafer was given and received is high. Furthermore, the numberof carrier arms is a major point governing the size of the carrier unit,so the carrier path becomes long when giving and receiving of the waferis performed between the carrier arms on the carrier path. Additionally,a floor area (foot print) that is needed for the exposure apparatus alsobecomes large.

In wafer steppers, the alignment of an exposure field to the reticlebeing imaged affects the success of the circuit of that field. In ascanning exposure system, the reticle and wafer are moved simultaneouslyand scanned across one another during the exposure sequence.

To attain high accuracy, the stage should be isolated from mechanicaldisturbances. This is achieved by employing electromagnetic forces toposition and move the stage. It should also have high control bandwidth,which requires that the stage be a light structure with no moving parts.Furthermore, the stage should be free from excessive heat generationwhich might cause interferometer interference or mechanical changes thatcompromise alignment accuracy.

Commutatorless electromagnetic alignment apparatus such as the onesdisclosed in U.S. Pat. Nos. 4,506,204, 4,506,205 and 4,507,597 are notfeasible because they require the manufacture of large magnet and coilassemblies that are not commercially available. The weight of the stageand the heat generated also render these designs inappropriate for highaccuracy applications.

An improvement over these commutatorless apparatus was disclosed in U.S.Pat. No. 4,592,858, which employs a conventional XY mechanically guidedsub-stage to provide the large displacement motion in a plane, therebyeliminating the need for large magnet and coil assemblies. Theelectromagnetic means mounted on the sub-stage isolates the stage frommechanical disturbances. Nevertheless, the combined weight of thesub-stage and stage still results in low control bandwidth, and the heatgenerated by the electromagnetic elements supporting the stage is stillsubstantial.

Even though the current apparatus using commutated electromagnetic meansis a significant improvement over prior commutatorless apparatus, theproblems of low control bandwidth and interferometer interferencepersist. In such an apparatus, a sub-stage is moved magnetically in onelinear direction and the commutated electromagnetic means mounted on thesub-stage in turn moves the stage in the normal direction. The sub-stageis heavy because it carries the magnet tracks to move the stage.Moreover, heat dissipation on the stage compromises interferometeraccuracy.

It is also well known to move a movable member (stage) in one longlinear direction (e.g. more than 10 cm) by using two of the linearmotors in parallel where coil and magnet are combined. In this case, thestage is guided by some sort of a linear guiding member and driven inone linear direction by a linear motor installed parallel to the guidingmember. When driving the stage only to the extent of extremely smallstroke, the guideless structure based on the combination of severalelectromagnetic actuators, as disclosed in the prior art mentionedbefore, can be adopted. However, in order to move the guideless stage bya long distance in one linear direction, a specially structuredelectromagnetic actuator as in the prior art becomes necessary, causingthe size of the apparatus to become larger, and as a result, generatinga problem of consuming more electricity.

SUMMARY OF THE INVENTION

It is an object of the present invention to make it possible for aguideless stage to move with a long linear motion using electromagneticforce, and to provide a light weight apparatus in which low inertia andhigh response are achieved.

It is another object of the present invention to provide a guidelessstage apparatus using commercially available regular linear motors aselectromagnetic actuators for one linear direction motion.

It is another object of the present invention to provide a guidelessstage apparatus capable of active and precise position control for smalldisplacements without any contact in the direction orthogonal to thelong linear motion direction.

It is another object of the present invention to provide a completelynon-contact stage apparatus by providing a movable member (stage body)that moves in one linear direction and a second movable member thatmoves sequentially in the same direction, constantly keeping a certainspace therebetween, and providing the electromagnetic force (action andreaction forces) in the direction orthogonal to the linear directionbetween this second movable member and the stage body.

It is another object of the present invention to provide a non-contactstage apparatus capable of preventing the positioning and runningaccuracy from deteriorating by changing tension of various cables andtubes to be connected to the non-contact stage body that moves as itsupports an object.

It is another object of the present invention to provide a non-contactapparatus that is short in its height, by arranging the first movablemember and the second movable member in parallel, which move in theopposite linear direction to one another.

It is another object of the present invention to provide an apparatusthat is structured so as not to change the location of the center ofgravity of the entire apparatus even when the non-contact stage bodymoves in one linear direction.

Another object of this invention is to provide an exposure apparatusthat can perform an exposure with high accuracy by reducing the effectsof vibration on a projection optical system or the like that occurs whenthe wafer stage or the like is driven.

Another object of this invention is to provide an exposure apparatusthat suppresses the amount of heat generated by the driving part of thewafer stage, to perform positioning of the driving part of the waferstage with high accuracy, and to maintain the measurement stability of aposition measurement device or the like.

Another object of this invention is to provide an exposure apparatuswith high throughput that can carry a wafer to an exposure apparatuswithout temporarily fixing the wafer, and without giving and receivingof the wafer between wafer carrier arms.

In order to achieve the above and other objects, embodiments of thepresent invention may be constructed as follows.

An apparatus that is capable of high accuracy position and motioncontrol utilizes linear commutated motors to move a guideless stage inone long linear direction and to create small yaw rotation in a plane. Acarrier/follower holding a single voice coil motor (VCM) is controlledto approximately follow the stage in the direction of the long linearmotion. The VCM provides an electromagnetic force to move the stage forsmall displacements in the plane in a linear direction perpendicular tothe direction of the long linear motion to ensure proper alignment. Thisfollower design eliminates the problem of cable drag for the stage sincethe cables connected to the stage follow the stage via thecarrier/follower. Cables connecting the carrier/follower to externaldevices will have a certain amount of drag, but the stage is free fromsuch disturbances because the VCM on the carrier/follower acts as abuffer by preventing the transmission of mechanical disturbances to thestage.

According to one aspect of the invention, the linear commutated motorsare located on opposite sides of the stage and are mounted on a drivingframe. Each linear commutated motor includes a coil member and amagnetic member, one of which is mounted on one of the opposed sides ofthe stage, and the other of which is mounted on the driving frame. Bothmotors drive in the same direction. By driving the motors slightlydifferent amounts, small yaw rotation of the stage is produced.

In accordance with another aspect of the present invention, a movingcounter-weight is provided to preserve the location of the center ofgravity of the stage system during any stage motion by using theconservation of momentum principle. In an embodiment of the presentinvention, the drive frame carrying one member of each of the linearmotors is suspended above the base structure, and when the driveassembly applies an action force to the stage to move the stage in onedirection over the base structure, the driving frame moves in theopposite direction in response to the reaction force to substantiallymaintain the center of gravity of the apparatus. This apparatusessentially eliminates any reaction forces between the stage system andthe base structure on which the stage system is mounted, therebyfacilitating high acceleration while minimizing vibrational effects onthe system.

By restricting the stage motion to the three specified degrees offreedom, the apparatus is simple. By using electromagnetic componentsthat are commercially available, the apparatus design is easilyadaptable to changes in the size of the stage. This high accuracypositioning apparatus is ideally suited for use as a reticle scanner ina scanning exposure system by providing smooth and precise scanningmotion in one linear direction and ensuring accurate alignment bycontrolling small displacement motion perpendicular to the scanningdirection and small yaw rotation in the scanning plane.

An exposure apparatus according to another aspect of this inventionincludes a projection optical system support member that supports aprojection optical system, so that the projection optical system rotateswithin a specified area, taking a reference point as a center.Therefore, even if vibration from a substrate stage and a mask stage istransmitted to the projection optical system, the position relationshipbetween the object plane (mask) and the image plane (substrate) is notshifted. Thus, it is possible to prevent position shifting of thepattern to be transferred, and highly accurate exposure can beperformed.

Furthermore, a mask stage that moves a mask, a structural body thatsupports this mask stage and the projection optical system, and asubstrate stage that moves a substrate are provided. The projectionoptical system support part (the structural body) has at least threeflexible support members extending from the structural body, and theextending lines of each support member cross at the reference point. Inthis case, even if vibration is transmitted to the projection opticalsystem, the projection optical system is minutely rotated taking thereference point as a center. Therefore, it is possible to preventposition shifting of the pattern to be transferred to the substrate.Furthermore, the support members are flexible, so the minute vibrationcan be reduced and the deterioration of contrast of a pattern to beformed can be prevented.

An exposure apparatus according to another aspect of this inventioncontrols the mask base so that the mask base moves at a specified speedin a direction opposite to the moving direction of the mask stage. Thisreduces the effects to the structural body of the driving reaction ofthe mask stage. Additionally, the excitation of mechanical resonance iscontrolled, and the vibration transmitted to the structural body and theprojection optical system can be reduced. Therefore, exposure with ahigh accuracy can be performed.

In an exposure apparatus according to another aspect of this invention,by having an elastic member at both ends of a guide axis, when thesubstrate table performs constant velocity reciprocation on the guideaxis, the kinetic energy of the substrate table is converted topotential energy and is stored in the elastic members. Therefore, theenergy to be consumed when the substrate table is reciprocated atconstant velocity is mainly only the energy to be consumed in theviscosity resistance of the substrate table with respect to air. Theonly heat generated is the heat from when the elastic members aredeformed. Therefore, it is possible to control the heating amount of thedriving part when the substrate table moves at constant velocity.

Furthermore, when the elastic member has first magnetic members disposedat both ends of the guide axis and second magnetic members disposedcorresponding to the first magnetic members, by the attraction of thefirst and second magnetic members, when the substrate table isstill-positioned at an end of the guide axis, it is possible to reducethe thrust of the driving part of the substrate table required to opposethe resistance of the elastic member. Thus, the heating amount of thedriving part can be controlled when the substrate table isstill-positioned.

In an exposure apparatus according to another aspect of this invention,by controlling the length of the support legs that can be freelyextended and retracted in the support direction, the tilt angle of thesubstrate table and its position in the height direction can becontrolled, and highly accurate exposure can be performed as the surfaceof the substrate is aligned within the image plane.

Furthermore, when the mask and the substrate are synchronously and movedduring exposure, the tilt angle of the scanning surface of the substratestage of the structural body in the scanning direction, the tilt anglein the non-scanning direction, and the height are detected. When thesupport legs that can be freely extended and retracted are controlledbased upon the detection result, highly accurate scanning exposure canbe performed as the surface of the substrate is aligned within the imageplane.

Furthermore, when the rotation angle of the substrate stage about theoptical axis of the projection optical system and the position shiftingamount are detected, and the position of the mask stage or the substratestage is controlled based upon this detection result, the positioningbetween the surface of the substrate and the image plane can beperformed with high accuracy.

In an exposure apparatus according to another aspect of this invention,a visco-elastic body exists between the support member and thestructural body, so it is possible to reduce the vibration from thefloor on which the exposure device is disposed. Therefore, exposure canbe performed with high accuracy.

In an exposure apparatus according to another aspect of this invention,at least one groove is provided in the substrate table, and a substratecan be disposed on the substrate table without the substrate carrierarms contacting the substrate table. That is, there is an advantage suchthat the substrate can be carried into and out from the exposure device,without temporarily fixing and supporting the substrate on the substratetable, and throughput can be improved.

Furthermore, when the substrate carrier mechanism has at least twosubstrate carrier arms and substrate storage case support members, thesubstrate carrier arms can be freely moved in the three directions suchas a rotational direction about the optical axis of the projectionoptical system, the horizontal direction, and the vertical direction,and the substrate storage case support member can be freely moved in thevertical direction, there are advantages such that the substrate stagecan be moved below the substrate carrying-out arms or the substratecarrying-in arms, the substrate can be carried to the exposure devicewithout transferring the substrate between the substrate carrier arms,and the probability of problems occurring during the carrying and theprobability of foreign objects attaching to the wafer can be reduced.

Other aspects and features and advantages of the present invention willbecome more apparent upon a review of the following specification takenin conjunction with the accompanying drawings wherein similar charactersof reference indicate similar elements in each of the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of an apparatus in accordancewith an embodiment of the present invention.

FIG. 2 is a top plan view of the apparatus shown in FIG. 1.

FIG. 3 is an end elevational view of the structure shown in FIG. 2 takenalong line 3-3′ in the direction of the arrows.

FIG. 4A is an enlarged perspective, partially exploded view showing thecarrier/follower structure of FIG. 1 and exploded from the positioningguide.

FIG. 4B is an enlarged horizontal sectional view of a portion of thestructure shown in FIG. 5 taken along line 4B in the direction of thearrow.

FIG. 4C is an enlarged elevational sectional view of a portion of thestructure shown in FIG. 2 taken along line 4C in the direction of thearrow but with the voice coil motor removed.

FIG. 5 is an elevational sectional view of a portion of the structureshown in FIG. 2 taken along line 5-5′ in the direction of the arrows.

FIG. 6 is a block diagram schematically illustrating the sensing andcontrol systems for controlling the position of the stage.

FIG. 7 is a plan view, similar to FIG. 2, illustrating a preferredembodiment of the present invention.

FIG. 8 is an elevational sectional view of the structure shown in FIG. 7taken along line 8-8′ in the direction of the arrows.

FIGS. 9 and 10 are simplified schematic views similar to FIGS. 7 and 8and illustrating still another embodiment of the present invention.

FIG. 11 is a perspective view showing a schematic structure of aprojection exposure apparatus according to an embodiment of thisinvention.

FIG. 12 is a cross-sectional view taken through a part showing a methodof supporting the projection optical system of FIG. 11.

FIG. 13A is a plan view showing the wafer stage of FIG. 11. FIG. 13B isa cross-sectional view of FIG. 13A along line B-B. FIG. 13C is a frontview omitting part of FIG. 13A. FIG. 13D is a cross-sectional view ofFIG. 13A along line D-D.

FIG. 14 is a block diagram showing a structure of a controller thatcontrols a wafer table and a carrier.

FIGS. 15A-C are schematic diagrams that accompany an operationexplanation of a guide shaft and a guide member of the wafer table ofFIGS. 13A-C.

FIG. 16A is a diagram showing the speed of the wafer table when themoving speed of the wafer table is shifted to a constant speed on aguide axis without an elastic body. FIG. 16B is a diagram showing thrustof linear motors.

FIG. 17A is a diagram showing a speed curve of a wafer table that iscalculated assuming the case where an ideal wafer table withoutvibration is accelerated to a constant speed on a guide axis withsprings. FIG. 17B is a diagram showing thrust of linear motors which iscalculated assuming the case where a wafer table with vibration iscontrolled taking the speed curve of FIG. 17A as a speed governingvalue.

FIG. 18A is a diagram showing the speed when a wafer table isaccelerated to a constant speed using a guide axis with springs, takingthe speed curve of FIG. 17A as a speed governing value. FIG. 18B is adiagram showing thrust of a wafer table at that time and the thrustgenerated by linear motors.

FIG. 19A is a diagram showing a speed curve when a wafer table isaccelerated to a constant speed when a guide axis with springs in whicha spring constant is the optimum value is used. FIG. 19B is a diagramshowing thrust of the wafer table.

FIG. 20 is a diagram showing the resistance of the springs at the endsof a guide axis with springs.

FIGS. 21A-C are schematic diagrams that accompany the explanation of theoperation of the guide member and the guide shaft when a magnetic memberis further provided.

FIG. 22A is a diagram showing speed that is calculated assuming the casewhere an ideal wafer table without vibration is accelerated to aconstant speed on a guide axis provided with springs, steel plates, andmagnets. FIG. 22B is a diagram showing thrust of linear motorscalculated assuming the case where a wafer table with vibration iscontrolled taking the speed curve of FIG. 22A as a speed governingvalue.

FIG. 23A is a diagram showing the speed curve when a wafer table on aguide axis with steel plates and magnets is accelerated to a constantspeed, taking the speed curve of FIG. 22A as a speed governing value.FIG. 23B is a diagram showing thrust of the wafer table at that time,and the thrust of linear motors.

FIG. 24 is a diagram showing the resultant force between the resistanceof the spring and the attraction between the magnet and the steel plateat an end of the guide axis to which the steel plate and the magnet arefixed.

FIG. 25A is a schematic diagram showing a support leg that supports awafer table, and the vicinity thereof, by enlargement. FIG. 25B is aside view of FIG. 25A.

FIG. 26 is a block diagram showing a structure of a controller thatcontrols a reticle stage, a wafer stage, and a wafer base.

FIGS. 27A-B are diagrams explaining the operation of the wafer stagewhen a wafer is carried into or out from an exposure device.

FIGS. 28A-B are diagrams explaining the operation of a wafer carrier armwhen an already-exposed wafer is carried out from an exposure device.

FIGS. 29A-B are diagrams explaining the operation of a wafer carrier armwhen a non-exposed wafer is carried into an exposure device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

While the present invention has applicability generally toelectromagnetic alignment system, the preferred embodiments involve ascanning apparatus for a reticle stage as illustrated in FIGS. 1-6.

Referring now to the drawings, the positioning apparatus 10 of thepresent invention includes a base structure 12 above which a reticlestage 14 is suspended and moved as desired, a reticle stage positiontracking laser interferometer system 15, a position sensor 13 and aposition control system 16 operating from a CPU 16′ (see FIG. 6).

An elongate positioning guide 17 is mounted on the base 12, and supportbrackets 18 (two brackets in the illustrated embodiment) are movablysupported on the guide 17 such as by air bearings 20. The supportbrackets 18 are connected to a driving assembly 22 in the form of amagnetic track assembly or driving frame for driving the reticle stage14 in the X direction and small yaw rotation. The driving frame includesa pair of parallel spaced apart magnetic track arms 24 and 26 which areconnected together to form an open rectangle by cross arms 28 and 30. Inthe preferred embodiment, the driving frame 22 is movably supported onthe base structure 12 such as by air bearings 32 so that the frame isfree to move on the base structure in a direction aligned with thelongitudinal axis of the guide 17, the principal direction in which thescanning motion of the reticle stage is desired. As used herein “onedirection” or a “first direction” applies to movement of the frame 22 orthe reticle stage 14 either forward or backward in the X direction alonga line aligned with the longitudinal axis of the guide 17.

Referring now to FIGS. 1 and 3 to explain further in detail, theelongate guiding member 17 in the X direction has front and rear guidingsurfaces 17A and 17B, which are almost perpendicular to the surface 12Aof the base structure 12. The front guiding surface 17A is against therectangular driving frame 22 and guides the air bearing 20 which isfixed to the inner side of the support bracket 18. A support bracket 18is mounted on each end of the upper surface of the arm 24, which isparallel to the guiding member 17 of the driving frame 22. Furthermore,each support bracket 18 is formed in a book shape so as to straddle theguiding member 17 in the Y direction, and with the free end against therear guiding surface 17B of the rear side of the guiding member 17. Theair bearing 20′ is fixed inside the free end of the support brackets 18and against the rear guiding surface 17B. Therefore, each of the supportbrackets 18 is constrained in its displacement in the Y direction by theguiding member 17 and air bearings 20 and 20′ and is able to move onlyin the X direction.

Now according to the first embodiment of the present invention, the airbearings 32, which are fixed to the bottom surfaces of the fourrectangular parts of the driving frame 22, make an air layer leaving aconstant (several μm) between the pad surface and the surface 12A of thebase structure 12. The driving frame is buoyed up from the surface 12Aand supported perpendicularly (in the Z direction) by the air layer. Itwill be explained in detail later, but in FIG. 1, the carrier/follower60 shown positioned above the upper part of the elongate arm 24 ispositioned laterally in the Y direction by air bearings 66A and 66Bsupported by a bracket 62 against opposite surfaces 17A and 17B ofguiding member 17 and vertically in the Z direction by air bearings 66above the surface 12A of the base structure 12. Thus, thecarrier/follower 60 is positioned so as not to contact any part of thedriving frame 22. Accordingly, the driving frame 22 moves only in onelinear X direction, guided above the base surface 12A and laterally bythe guiding member 17.

Referring now to both FIG. 1 and FIG. 2, the structure of the reticlestage 14 and the driving frame 22 will be explained. The reticle stage14 includes a main body 42 on which the reticle 44 is positioned abovean opening 46. The reticle body 42 includes a pair of opposed sides 42Aand 42 b and is positioned or suspended above the base structure 12 suchas by air bearings 48. A plurality of interferometer mirrors 50 areprovided on the main body 42 of the reticle stage 14 for operation withthe laser interferometer position sensing system 15 (see FIG. 6) fordetermining the exact position of the reticle stage which is fed to theposition control system 16 in order to direct the appropriate drivesignals for moving the reticle stage 14 as desired.

Primary movement of the reticle stage 14 is accomplished with firstelectromagnetic drive assembly or means in the form of separate driveassemblies 52A and 52B (FIG. 2) on each of the opposed sides 42A and42B, respectively. The drive assemblies 52A and 52B include drive coils54A and 54B fixedly mounted on the reticle stage 14 at the sides 42A and42B, respectively, for cooperating with magnet tracks 56A and 56B on themagnet track arms 24 and 26, respectively, of the drive frame 22. Whilein the preferred embodiment of the invention the magnet coils aremounted on the reticle stage and the magnets are mounted on the driveframe 22, the positions of these elements of the electromagnetic driveassembly 52 could be reversed.

Here, the structure of the reticle stage 14 will be explained further indetail. As shown in FIG. 1, the stage body 42 is installed so that it isfree to move in the Y direction in the rectangular space inside thedriving frame 22. The air bearing 48 fixed under each of the fourcorners of the stage body 42 makes an extremely small air gap betweenthe pad surface and the base surface 12A, and buoys up and supports theentire stage 14 from the surface 12A. These air bearings 48 shouldpreferably be pre-loaded types with a recess for vacuum attraction tothe surface 12A.

As shown in FIG. 2, a rectangular opening 46 in the center of the stagebody 42 is provided so that the projected image of the pattern formed onthe reticle 44 can pass therethrough. In order for the projected imagevia the rectangular opening 46 to pass through the projection opticalsystem PL (see FIG. 5) which is installed below the rectangular opening,there is another opening 12B provided at the center part of the basestructure 12. The reticle 44 is loaded on the top surface of the stagebody by clamping members 42C, which are protrusively placed at fourpoints around the rectangular opening 46, and clamped by vacuumpressure.

The interferometer mirror 50Y, which is fixed near the side 42B of thestage body 42 near the arm 26, has a vertical elongate reflectingsurface in the X direction which length is somewhat longer than themovable stroke of the stage 14 in the X direction, and the laser beamLBY from the Y-axis interferometer is incident perpendicularly on thereflecting surface. In FIG. 2, the laser beam LBY is bent at a rightangle by the mirror 12D, which is fixed on the side of the basestructure 12.

Referring now to FIG. 3 as a partial cross-sectional drawing of the viewalong line 3-3′ in FIG. 2, the laser beam LBY which is incident on thereflecting surface of the interferometer mirror 50Y is placed so as tobe on the same plane as the bottom surface (the surface where thepattern is formed) of the reticle 44 which is mounted on the clampingmember 42C. Furthermore, in FIG. 3, the air bearing 20 on the end sideof the support brackets 18 against the guiding surface 17B of theguiding member 17 is also shown.

Referring once again to FIGS. 1 and 2, the laser beam LBX1 from theX1-axis interferometer is incident and reflected on the interferometermirror 50X1, and the laser beam LBX2 from the X2-axis interferometer isincident and reflected on the interferometer mirror 50X2. These twomirrors 50X1 and 50X2 are structured as corner tube type mirrors, andeven when the stage 14 is in yaw rotation, they always maintain theincident axis and reflecting axis of the laser beams parallel within theXY plane. Furthermore, the block 12C in FIG. 2 is an optical block, suchas a prism, to orient the laser beams LBX1 and LBX2 to each of themirrors 50X1 and 50X2, and is fixed to a part of the base structure 12.The corresponding block for the laser beam LBY is not shown.

In FIG. 2, the distance BL in the Y direction between each of the centerlines of the two laser beams LBX1 and LBX2 is the length of the baseline used to calculate the amount of yaw rotation. Accordingly, thevalue of the difference between the measured value ΔX1 in the Xdirection of the X1-axis interferometer and the measured value ΔX2 inthe X direction of the X2-axis interferometer divided by the base linelength BL is the approximate amount of yaw rotation in an extremelysmall range. Also, half the value of the sum of ΔX1 and ΔX2 representsthe X coordinate position of the entire stage 14. These calculations areperformed by a high speed digital processor in the position controlsystem 16 shown in FIG. 6.

Furthermore, the center lines of each of the laser beams LBX1 and LBX2are set on the same surface where the pattern is formed on the reticle44. The extension of the line GX, which is shown in FIG. 2 and dividesin half the space between each of the center lines of laser beams LBX1and LBX2, and the extension of the laser beam LBY intersect within thesame surface where the pattern is formed. Additionally, the optical axisAX (see FIGS. 1 and 5) also crosses at this intersection as shown inFIG. 1. In FIG. 1, a slit shaped illumination field ILS which includesthe optical axis AX is shown over the reticle 44, and the pattern imageof the reticle 44 is scanned and exposed onto the photosensitivesubstrate via the projection optical system PL.

Furthermore, there are two rectangular blocks 90A and 90B fixed on theside 42A of the stage body 42 in FIGS. 1 and 2. These blocks 90A and 90Bare to receive the driving force in the Y direction from the secondelectromagnetic actuator 70 which is mounted on the carrier/follower 60.Details will be explained below.

The driving coils 54A and 54B which are fixed on the both sides of thestage body 42 are formed flat parallel to the XY plane, and pass throughthe magnetic flux space in the slot which extends in the X direction ofthe magnetic tracks 56A and 56B without any contact. The assembly of thedriving coil 54 and the magnetic track 56 used in the present embodimentis a commercially easily accessible linear motor for general purposes,and it could be either with or without a commutator.

Here, considering the actual design, the moving stroke of the reticlestage 14 is mostly determined by the size of the reticle 44 (the amountof movement required at the time of scanning for exposure and the amountof movement required at the time of removal of the reticle from theillumination optical system to change the reticle). In the case of thepresent embodiment, when a 6-inch reticle is used, the moving stroke isabout 30 cm.

As mentioned before, the driving frame 22 and the stage 14 areindependently buoyed up and supported on the base surface 12A, and atthe same time, magnetic action and reaction forces are applied to oneanother in the X direction only by the linear motor 52. Because of that,the law of the conservation of momentum is seen between the drivingframe 22 and the stage 14.

Now, suppose the weight of the entire reticle stage 14 is about onefifth of the entire weight of the frame 22 which includes the supportbrackets 18. Then, the forward movement of 30 cm of the stage 14 in theX direction makes the driving frame 22 move by 6 cm backwards in the Xdirection. This means that the location of the center of gravity of theapparatus on the base structure 12 is essentially fixed in the Xdirection. In the Y direction, there is no movement of any heavy object.Therefore, the change in the location of the center of gravity in the Ydirection is also relatively fixed.

The stage 14 can be moved in the X direction as described above, but themoving coils (54A, 54B) and the stators (56A, 56B) of the linear motors52 will interfere with each other (collide) in the Y direction withoutan X direction actuator. Therefore, the carrier/follower 60 and thesecond electromagnetic actuator 70 are provided to control the stage 14in the Y direction. Their structures will be explained with reference toFIGS. 1, 2, 3 and 5.

As shown in FIG. 1, the carrier/follower 60 is movably installed in theY direction via the hook-like support bracket 62 which straddles overthe guiding member 17. Furthermore as evident from FIG. 2, thecarrier/follower 60 is placed above the arm 24, so as to maintain acertain space between the stage 14 (the body 42) and the arm 24,respectively. One end 60E of the carrier/follower 60, is substantiallyprotruding inward (toward the stage body 42) over the arm 24. Insidethis end part 60E is fixed a driving coil 68 (FIGS. 4A and 6) (havingthe same shape as the coil 54) which enters a slot space of the magnetictrack 56A.

Furthermore, the bracket 62 supported by air bearing 66A (see FIGS. 2,3, 4A and 5) against the guiding surface 17A of the guiding member 17 isfixed in the space between the guiding member 17 of the carrier/follower60 and the arm 24. The air bearing 66 that buoys up and supports thecarrier/follower 60 on the base surface 12A is also shown in FIG. 3.

The air bearing 66B against the guiding surface 17B of the guidingmember 17 is also fixed to the free end of support bracket 62 on theother side of the hook from air bearing 66A with guiding member 17therebetween.

Now, as evident from FIG. 5, the carrier/follower 60 is arranged so asto keep certain spaces with respect to both the magnetic track 56A andthe stage body 42 in the Y and Z directions, respectively. Shown in FIG.5 are the projection optical system PL and column rod CB to support thebase structure 12 above the projection optical system PL. Such anarrangement is typical for a projection aligner, and unnecessary shiftof the center of gravity of the structures above the base structure 12would cause a lateral shift (mechanical distortion) between the columnrod CB and the projection optical system PL, and thus result in adeflection of the image on the photosensitive substrate at the time ofexposure. Hence, the merit of the device as in the present embodimentwhere the motion of the stage 14 does not shift the center of gravityabove the base structure 12 is substantial.

Furthermore referring now to FIG. 4A, the structure of thecarrier/follower 60 will be explained. In FIG. 4A, the carrier/follower60 is disassembled into two parts, 60A and 60B, for the sake offacilitating one's understanding. As evident from FIG. 4A, the drivingcoil 68 that moves the carrier/follower 60 itself in the X direction isfixed at the lower part of the end 60E of the carrier/follower 60.Furthermore, the air bearing 66C is placed against the base structure12A on the bottom surface of the end 60E and helps to buoy up thecarrier/follower 60.

Hence the carrier/follower 60 is supported in the Z direction with threepoints—the two air bearings 66 and one air bearing 66C—and isconstrained in the Y direction for movement in the X direction by airbearings 66A and 66B. What is important in this structure is that thesecond electromagnetic actuator 70 is arranged back to back with thesupport bracket 62 so that when the actuator generates the driving forcein the Y direction, reaction forces in the Y direction between the stage14 and the carrier/follower 60 actively act upon the air bearings 66Aand 66B which are fixed inside the support bracket 62. In other words,arranging the actuator 70 and the air bearings 66A, 66B on the lineparallel to the Y-axis in the XY plane helps prevent the generation ofunwanted stress, which might deform the carrier/follower 60 mechanicallywhen the actuator 70 is in operation. Conversely, it means that it ispossible to reduce the weight of the carrier/follower 60.

As evident from FIGS. 2, 4A and 4C described above, the magnetic track56A in the arm 24 of the driving frame 22 provides magnetic flux for thedriving coil 54A on the stage body 42 side, and concurrently providesmagnetic flux for the driving coil 68 for the carrier/follower 60. Asfor the air bearings 66A, 66B and 66C, a vacuum pre-loaded type ispreferable, since the carrier/follower 60 is light. Besides the vacuumpre-loaded type, a magnetic pre-loaded type is also acceptable.

Next with reference to FIGS. 3, 4B and 5, the second actuator mounted onthe carrier/follower 60 will be explained. A second electromagneticdrive assembly in the form of a voice coil motor 70 is made up of avoice coil 74 attached to the main body 42 of the reticle stage 14 and amagnet 72 attached to the carrier/follower 60 to move the stage 14 forsmall displacements in the Y direction in the plane of travel of thestage 14 orthogonal to the X direction long linear motion produced bythe driving assembly 22. The positions of the coil 74 and magnet 72could be reversed. A schematic structure of the voice coil motor (VCM)70 is as shown in FIGS. 3 and 5, and the detailed structure is shown inFIG. 4B. FIG. 4B is a cross-sectional view of the VCM 70 sectioned atthe horizontal plane shown with an arrow 4B in FIG. 5. In FIG. 4B, themagnets 72 of the VCM 70 are fixed onto the carrier/follower 60 side.The coil of the VCM 70 comprises the coil body 74A and its supportingpart 74B. The supporting part 74B is fixed to a connecting plate 92 (aplate vertical to the XY plane) which is rigidly laid across the tworectangular blocks 90A and 90B. A center line KX of the VCM 70 shows thedirection of the driving force of the coil 74, and when an electriccurrent flows through the coil body 74A, the coil 74 displaces intoeither positive or negative movement in the Y direction in accordancewith the direction of the current, and generates a force correspondingto the amount of the current. Normally, in a commonly used VCM, aring-like damper or bellows are provided between the coil and magnet soas to keep the gap between the coil and magnet, but according to thepresent embodiment, that gap is kept by a follow-up motion of thecarrier/follower 60, and therefore, such supporting elements as a damperor bellows are not necessary.

In the present embodiment, capacitance gap sensors 13A and 13B areprovided as a positioning sensor 13 (see FIG. 6) as shown in FIG. 4B. InFIG. 4B, electrodes for capacitance sensors are placed so as to detectthe change in the gap in the X direction between the side surface of therectangular blocks 90A and 90B facing each other in the X direction andthe side surface of a case 70′ of the VCM 70. Such a positioning sensor13 can be placed anywhere as far as it can detect the gap change in theY direction between the carrier/follower 60 and the stage 14 (or thebody 42). Furthermore, the type of the sensor can be any of anon-contact type such as, for example, photoelectric, inductive,ultrasonic, or air-micro system.

The case 70′ in FIG. 4B is formed with the carrier/follower 60 in one,and placed (spatially) so as not to contact any member on the reticlestage 14 side. As for the gap between the case 70′ and the rectangularblocks 90A and 90B in the X direction (scanning direction), when the gapon the sensor 13A side becomes wider, the gap on the sensor 13B sidebecomes smaller. Therefore, if the difference between the measured gapvalue by the sensor 13A and the measured gap value by the sensor 13B isobtained by either digital operation or analog operation, and a directservo (feedback) control system which controls the driving current ofthe driving coil 68 for the carrier/follower 60 is designed using aservo driving circuit which makes the gap difference zero, then thecarrier/follower 60 will automatically perform a follow-up movement inthe X direction always keeping a certain space to the stage body 42.Alternatively, it is also possible to design an indirect servo controlsystem which controls an electric current flow to the driving coil 68,with the operation of position control system 16 in FIG. 6 using themeasured gap value obtained only from one of the sensors and the Xcoordinate position of the stage 14 measured from the X axisinterferometer, without using the two gap sensors 13A and 13Bdifferentially.

In the VCM 70 as described in FIG. 4B, the gap between the coil body 74Aand the magnet 72 in the X direction (non-energizing direction) is inactuality about 2-3 mm. Therefore, a follow-up accuracy of thecarrier/follower 60 with respect to the stage body 42 would beacceptable at around ±0.5-1 mm. This accuracy depends on how much of theyaw rotation of the stage body is allowed, and also depends on thelength of the line in the KX direction (energizing direction) of thecoil body 74A of the VCM 70. Furthermore, the degree of the accuracy forthis can be substantially lower than the precise positioning accuracyfor the stage body 42 using an interferometer (e.g., ±0.03 μm supposingthe resolution of the interferometer is 0.01 μm). This means that theservo system for a follower can be designed fairly simply, and theamount of cost to install the follower control system would be small.Furthermore, the line KX in FIG. 4B is set so as to go through thecenter of gravity of the entire stage 14 on the XY plane, and each ofcenters of the pair of the air bearings 66A and 66B provided inside thesupport brackets 62 shown in FIG. 4 is also positioned on the line KX inthe XY plane.

FIG. 4C is a cross-sectional drawing of the part which includes theguiding member 17, the carrier/follower 60, and the magnetic track 56Asectioned from the direction of the arrow 4C in FIG. 2. The arm 24storing the magnetic track 56A is buoyed up and supported on the basesurface 12A by the air bearing 32, and the carrier/follower 60 is buoyedup and supported on the base surface 12A by the air bearing 66. At thistime, the height of the air bearing 48 at the bottom surface of thestage body 42 (see FIGS. 3 or 5) and the height of the air bearing 32are determined so as to place the driving coil 54A on the stage body 42side keeping a 2-3 mm gap in the Z direction in the slot space of themagnetic track 56A.

Each of the spaces between the carrier/follower 60 and the arm 24 in theZ and Y directions hardly changes because they are both guided by thecommon guiding member 17 and the base surface 12A. Furthermore, even ifthere is a difference in the height in the Z direction between the parton the base surface 12A where the air bearing 32 at the bottom surfaceof the driving frame 22 (arm 24) is guided and the part on the basesurface 12A where the air bearing 48 at the bottom surface of the stagebody is guided, as long as the difference is precisely constant withinthe moving stroke, the gap in the Z direction between the magnetic track56A and the driving coil 54A is also maintained constant.

Furthermore, since the driving coil 68 for the carrier/follower 60 isoriginally fixed to the carrier/follower 60, it is arranged, maintaininga certain gap of 2-3 mm above and below in the slot space of themagnetic track 56A. The driving coil 68 hardly shifts in the Y directionwith respect to the magnetic track 56A.

Cables 82 (see FIG. 2) are provided for directing the signals to thedrive coils 54A and 54B on stage 14, the voice coil motor coil 74 andthe carrier/follower drive coil 68, and these cables 82 are mounted onthe carrier/follower 60 and guide 17 thereby eliminating drag on thereticle stage 14. The voice coil motor 70 acts as a buffer by preventingtransmission of external mechanical disturbances to the stage 14.

Therefore, referring now to FIGS. 2 and 4A, the cable issues will bedescribed further in detail. As shown in FIG. 2, a connector 80 whichconnects wires of the electric system and tubes of the air pressure andthe vacuum system (hereafter called “cables”) is mounted on the basestructure 12 on one end of the guiding member 17. The connector 80connects a cable 81 from the external control system (including thecontrol system of the air pressure and the vacuum systems besides theelectric system control system shown in FIG. 6) to a flexible cable 82.The cable 82 is further connected to the end part 60E of thecarrier/follower 60, and electric system wires and the air pressure andthe vacuum system tubes necessary for the stage body 42 are distributedas the cable 83.

As mentioned before, the VCM 70 works to cancel a cable's drag or aninfluence by tension, but sometimes its influence appears as a moment inan unexpected direction between the carrier/follower 60 and the stagebody 42. In other words, the tension of the cable 82 gives thecarrier/follower 60 a force to rotate the guiding surface of the guidingmember 17 or the base surface 12A, and the tension of the cable 83 givesa force to the carrier/follower 60 and the stage body to rotaterelatively.

One of these moments, the constituent which shifts the carrier/follower60, is not problematic, but the one which shifts the stage body in X, Y,or θ direction (yaw rotation direction) could affect the alignment oroverlay accuracy. As for the X and θ directions, shifts can be correctedby a consecutive drive by the two linear motors (54A, 56A, 54B, 56B),and as for in the Y direction, the shift can be corrected by the VCM 70.In the present embodiment, since the weight of the entire stage 14 canbe reduced substantially, the response of the motion of the stage 14 byVCM 70 in the Y direction and the response by the linear motor in X andθ directions will be extremely high in cooperation with the completelynon-contact guideless structure. Furthermore, even when a microvibration (micron order) is generated in the carrier/follower 60 and itis transferred to the stage 14 via the cable 83, the vibration (fromseveral Hz to tens of Hz) can be sufficiently canceled by the abovementioned high response.

Now, FIG. 4A shows how each of the cables is distributed at thecarrier/follower 60. Each of the driving signals to the driving coils54A, 54B for the stage body 42 and the driving coil 74 of the VCM 70 andthe detection signal from the position sensor 13 (the gap sensors 13A,13B) go through the electric system wire 82A from the connector 80. Thepressure gas and the vacuum to each of the air bearings 48 and 66 gothrough the pneumatic system tube 82B from the connector 80. On theother hand, the driving signal to the driving coils 54A and 54B goesthrough the electric system wire 83A which is connected to the stagebody 42, and the pressurized gas for the air bearing 48 and the vacuumfor the clamping member 42C go through the pneumatic system hoses 83B.

Furthermore, it is preferable to have a separate line for the pneumaticsystem for the air bearings 20, 20′ and 32 of the driving frame 22,independent of the one shown in FIG. 2. Also, as shown in FIG. 4A, incase the tension or vibration of the cable 83 cannot be prevented, it isadvisable to arrange the cable 83 so as to limit the moment by thetension or vibration the stage body 42 receives only to the Y directionas much as possible. In that case, the moment can be canceled only bythe VCM 70 with the highest response.

Referring now to FIGS. 1, 2 and 6, the positioning of the reticle stage14 is accomplished first knowing its existing position utilizing thelaser interferometer system 15. Drive signals are sent to the reticlestage drive coils 54A and 54B for driving the stage 14 in the Xdirection. A difference in the resulting drive to the opposite sides 42Aand 42B of the reticle stage 14 will produce small yaw rotation of thereticle stage 14. An appropriate drive signal to the voice coil 72 ofvoice coil motor 70 produces small displacements of the reticle stage 14in the Y direction. As the position of the reticle stage 14 changes, adrive signal is sent to the carrier/follower coil 68 causing thecarrier/follower 60 to follow the reticle stage 14. Resulting reactionforces to the applied drive forces will move the magnetic track assemblyor drive frame 22 in a direction opposite to the movement of the reticlestage 14 to substantially maintain the center of gravity of theapparatus. It will be appreciated that the counter-weight or reactionmovement of the magnetic track assembly 22 need not be included in theapparatus in which case the magnetic track assembly 22 could be fixedlymounted on the base 12.

As described above, in order to control the stage system according tothe present embodiment, a control system as shown in FIG. 6 isinstalled. This control system in FIG. 6 will be further explained indetail here. X1 driving coil and X2 driving coil composed as the drivingcoils 54A and 54B of two linear motors respectively, and Y driving coilcomposed as the driving coil 72 of the VCM 70 are placed in the reticlestage 14, and the driving coil 68 is placed in the carrier/follower 60.Each of these driving coils is driven in response to the driving signalsSX1, SX2, SY1 and SΔX, respectively, from the position control system16. The laser interferometer system 15 which measures the coordinatesposition of the stage 14 comprises the Y axis interferometer whichsends/receives the beam LBY, the X1 axis interferometer whichsends/receives the beam LBX1, and the X2 axis interferometer whichsends/receives the beam LBX2, and they send position information foreach of the directions of the axes, IFY, IFX1, IFX2 to the positioncontrol system 16. The position control system 16 sends two drivingsignals SX1 and SX2 to the driving coils 54A and 54B so that thedifference between the position information IFX1 and IFX2 in the Xdirection will become a preset value, or in other words, the yawrotation of the reticle stage 14 is maintained at the specified amount.Thus, the yaw rotation (in θ direction) positioning by the beams LBX1and LBX2, X1 axis and X2 axis interferometers, the position controlsystem 16, and the driving signals SX1 and SX2 is constantly beingconducted, once the reticle 44 is aligned on the stage body 42, needlessto mention the time of the exposure.

Furthermore, the control system 16, which obtained the currentcoordinate position of the stage 14 in the X direction from the averageof the sum of position information IFX1 and IFX2 in the X direction,sends the driving signals SX1, SX2 to the driving coils 54A and 54B,respectively, based on the various commands from the Host CPU 16′ andthe information CD for the parameters. Especially when scanning exposureis in motion, it is necessary to move the stage 14 straight in the Xdirection while correcting the yaw rotation, and the control system 16controls the two driving coils 54A and 54B to give the same or slightlydifferent forces as needed.

Furthermore, the position information IFY from the Y axis interferometeris also sent to the control system 16, and the control system 16 sendsan optimum driving signal SΔX to the driving coil 68 of thecarrier/follower 60. At that time, the control system 16 receives thedetection signal S_(pd) from the position sensor 13 which measures thespace between the reticle stage 14 and the carrier/follower 60 in the Xdirection, and sends a necessary signal SΔX to make the signal S_(pd)into the preset value as mentioned before. The follow-up accuracy forthe carrier/follower 60 is not so strict that the detection signalS_(pd) of the control system 16 does not have to be evaluated strictlyeither. For example, when controlling the motion by reading the positioninformation IFY, IFX1, IFX2 every 1 millisecond from each of theinterferometers, the high speed processor in the control system 16samples the current of the detection signal S_(pd) each time, determineswhether the value is large or small compared to the reference value(acknowledge the direction), and if the deviation surpasses a certainpoint, the signal SΔX in proportion to the deviation can be sent to thedriving coil 68. Furthermore as mentioned before, it is also acceptableto install a control system 95 which directly servo controls the drivingcoil 68, and directly controls the follow-up motion of thecarrier/follower 60 without going through the position control system16.

Since the moving stage system as shown has no attachment to constrain itin the X direction, small influences may cause the system to drifttoward the positive or negative X direction. This would cause certainparts to collide after this imbalance became excessive. The influencesinclude cable forces, imprecise leveling of the base reference surface12A or friction between components. One simple method is to use weakbumpers (not shown) to prevent excessive travel of the drive assembly22. Another simple method is to turn off the air to one or more of theair bearings (32, 20) used to guide the drive assembly 22 when the driveassembly reaches close to the end of the stroke. The air bearing(s) canbe turned on when the drive begins to move back in the oppositedirection.

More precise methods require monitoring the position of the driveassembly by a measuring device (not shown) and applying a driving forceto restore and maintain the correct position. The accuracy of themeasuring device need not be precise, but on the order of 0.1 to 1.0 mm.The driving force can be obtained by using another linear motor (notshown) attached to the drive assembly 22, or another motor that iscoupled to the drive assembly.

Finally, the one or more air bearings (66, 66A, 66B) of thecarrier/follower 60 can be turned off to act as a brake during idleperiods of the stage 42. If the coil 68 of the carrier/follower 60 isenergized with the carrier/follower 60 in the braked condition, thedrive assembly will be driven and accelerated. Thus, the positioncontrol system 16 monitors the location of the drive assembly 22. Whenthe drive assembly drifts out of position, the drive assembly isrepositioned with sufficient accuracy by intermittently using the coil68 of the carrier/follower 60.

In the first embodiment of the present invention, the driving frame 22which functions as a counter weight is installed in order to prevent thecenter of gravity of the entire system from shifting, and was made tomove in the opposite direction from the stage body 42. However, when thestructures in FIGS. 1-5 are applied to a system where the shift of thecenter of gravity is not a major problem, it is also acceptable to fixthe driving frame 22 on the base structure 12 together. In that case,except for the problem regarding the center of gravity, some of theeffects and function can be applied without making any changes.

This invention provides a stage which can be used for high accuracyposition and motion control in three degrees of freedom in one plane:(1) long linear motion; (2) short linear motion perpendicular to thelong linear motion; and (3) small yaw rotation. The stage is isolatedfrom mechanical disturbances of surrounding structures by utilizingelectromagnetic forces as the stage driver. By further using a structurefor this guideless stage, a high control bandwidth is attained. Thesetwo factors contribute to achieve the smooth and accurate operation ofthe stage.

Bearing in mind the description of the embodiment illustrated in FIGS.1-6, one preferred embodiment of the present invention is illustrated inFIGS. 7 and 8, wherein the last two digits of the numbered elements aresimilar to the corresponding two digit numbered elements in FIGS. 1-5.

In FIGS. 7 and 8, differing from the previous first embodiment, thedriving frame which functions as a counter weight is removed, and eachof the magnet tracks 156A and 156B of the two linear motors is rigidlymounted onto the base structure 112. The stage body 147 which movesstraight in the X direction is placed between the two magnetic tracks156A and 156B. As shown in FIG. 8, an opening 112B is formed in the basestructure 112, and the stage body 142 is arranged so as to straddle theopening 112B in the Y direction. There are four pre-loaded air bearings148 fixed on the bottom surface at both ends of the stage body 142 inthe Y direction, and they buoy up and support the stage body 142 againstthe base surface 112A.

Furthermore, according to the present embodiment, the reticle 144 isclamped and supported on a reticle chuck plate 143 which is separatelyplaced on the stage body 142. The straight mirror 150Y for the Y axislaser interferometer and two corner mirrors 150X1, 150X2 for the X axislaser interferometer are mounted on the reticle chuck plate 143. Thedriving coils 154A and 154B are horizontally fixed at both ends of thestage body 142 in the Y direction with respect to the magnetic tracks156A and 156B, and due to the control subsystem previously described,make the stage body 142 run straight in the X direction and yaw only toan extremely small amount.

As evident from FIG. 8, the magnetic track 156B of the right side of thelinear motor and the magnetic track 156A of the left side of the linearmotor are arranged so as to have a difference in level in the Zdirection between them. In other words, the bottom surface of both endsin the direction of the long axis of the magnetic track 156 on the leftside is, as shown in FIG. 7, elevated by a certain amount with a blockmember 155 against the base surface 112A. The carrier/follower 160 wherethe VCM 170 is fixed is arranged in the space below the elevatedmagnetic track 156A.

The carrier/follower 160 is buoyed up and supported by the pre-loadedair bearings 166 (at 2 points) on the base surface 112A′ of the basestructure 112 which is one level lower. Furthermore, two pre-loaded airbearings 164 against the vertical guiding surface 117A of the straightguiding member 117, which is mounted onto the base structure 112, arefixed on the side surface of the carrier/follower 160. Thiscarrier/follower 160 is different from the one in FIG. 4A according tothe previous embodiment, and the driving coil 168 (FIG. 7) for thecarrier/follower 160 is fixed horizontally to the part which extendsvertically from the bottom of the carrier/follower 160, and positionedin the magnetic flux slot of the magnetic track 156A without anycontact. The carrier/follower 160 is arranged so as not to contact anypart of the magnetic track 156A within the range of the moving stroke,and has the VCM 170 which positions the stage body 142 precisely in theY direction.

Furthermore, in FIG. 7, the air bearing 166 which buoys up and supportsthe carrier/follower 160 is provided under the VCM 170. The follow-upmotion to the stage body 142 of the carrier/follower 160 is also donebased on the detection signal from the position sensor 13 as in theprevious embodiment.

In the second embodiment structured as above, there is an inconveniencewhere the center of gravity of the entire system shifts in accordancewith the shift of the stage body 142 in the X direction, since there issubstantially no member which functions as a counter weight. It is,however, possible to position the stage body 142 precisely in the Ydirection with non-contact electromagnetic force by the VCM 170 by wayof following the stage body 142 without any contact using thecarrier/follower 160. Furthermore, since the two linear motors arearranged with a difference in the level in the Z direction between them,there is a merit where the sum of the vectors of the force momentgenerated by each of the linear motors can be minimized at the center ofgravity of the entire reticle stage because the force moment of each ofthe linear motors substantially cancels with the other.

Furthermore, since an elongated axis of action (the line KX in FIG. 4B)of the VCM 170 is arranged so as to pass through the center of gravityof the entire structure of the stage not only on the XY plane but alsoin the Z direction, it is more difficult for the driving force of theVCM 170 to give unnecessary moment to the stage body 142. Furthermore,since the method of connecting the cables 82, 83 via thecarrier/follower 160 can be applied in the same manner as in the firstembodiment, the problem regarding the cables in the completelynon-contact guideless stage is also improved.

The same guideless principle can be employed in another embodiment. Forexample, in schematic FIGS. 9 and 10, the stage 242, supported on abases 212, is driven in the long X direction by a single moving coil 254moving within a single magnetic track 256. The magnetic track is rigidlyattached to the base 212. The center of the coil is located close to thecenter of gravity of the stage 242. To move the stage in the Ydirection, a pair of VCMs (274A, 274B, 272A, 272B) are energized toprovide an acceleration force in the Y direction. To control yaw, thecoils 274A and 274B are energized differentially under control of theelectronics subsystem. The VCM magnets (272A, 272B) are attached to acarrier/follower stage 260. The carrier/follower stage 260 is guided anddriven like the first embodiment previously described. This alternativeembodiment can be utilized for a wafer stage. Where it is utilized for areticle stage the reticle can be positioned to one side of the coil 254and track 256, and if desired to maintain the center of gravity of thestage 242 passing through the coil 254 and track 256, a compensatingopening in the stage 242 can be provided on the opposite side of thecoil 254 and track 256 from the reticle.

Merits gained from each of the embodiments can be roughly listed asfollows. To preserve accuracy, the carrier/follower design eliminatesthe problem of cable drag for the stage since the cables connected tothe stage follow the stage via the carrier/follower. Cables connectingthe carrier/follower to external devices will have a certain amount ofdrag, but the stage is free from such disturbances since there is nodirect connection to the carrier/follower which acts as a buffer bydenying the transmission of mechanical disturbances to the stage.

Furthermore, the counter-weight design preserves the location of thecenter of gravity of the stage system during any stage motion in thelong stroke direction by using the conservation of momentum principle.This apparatus essentially eliminates any reaction forces between thestage system and the base structure on which the stage system ismounted, thereby facilitating high acceleration while minimizingvibrational effects on the system.

In addition, because the stage is designed for limited motion in thethree degrees of freedom as described, the stage is substantiallysimpler than those which are designed for full range motions in allthree degrees of freedom. Moreover, unlike a commutatorless apparatus,the instant invention uses electromagnetic components that arecommercially available. Because this invention does not requirecustom-made electromagnetic components which become increasinglydifficult to manufacture as the size and stroke of the stage increases,this invention is easily adaptable to changes in the size or stroke ofthe stage.

The embodiment with the single linear motor eliminates the second linearmotor and achieves yaw correction using two VCMs.

The following explains another embodiment of this invention withreference to FIGS. 11-29B. In this example, the invention is applied toa step-and-scan type projection exposure apparatus.

FIG. 11 shows a projection apparatus of this example. In this figure,during exposure, exposure light such as i rays of a mercury lamp,excimer laser light or the like such as KrF, ArF, F₂, or the like froman illumination optical system (not depicted) illuminates anillumination area of a pattern face of a reticle 301. Furthermore, apattern image within the illumination area of the reticle 301 isprojected and exposed on the top of the wafer 303 on which photoresistis coated, at a predetermined projection magnification β (β is normally¼, ⅕, or the like) through a projection optical system 302. Hereafter,an explanation is given with the Z-axis defined as being parallel to anoptical axis AX of the projection optical system 302 in a non-vibratingstate, and with the X-axis and Y-axis defining a perpendicularcoordinate system within a plane perpendicular to the optical axis AX.

First, the reticle 301 is held on the reticle stage 304, and when thereticle stage 304 continuously moves in the X direction (scanningdirection) by a linear motor method on the reticle base 309, amicro-adjustment of the position of the reticle 301 is performed withinthe XY plane. The two-dimensional position of the reticle stage 304(reticle 301) is measured by moving mirrors 343X and 343Y and laserinterferometers 318X and 318Y on the reticle stage 304. This measuredvalue is supplied to a main controller 350 comprising a computer thatcontrols an operation of the device as a whole. The main controller 350controls the position and the moving speed of the reticle stage 4through the reticle stage controller 352, based upon the measured value.

Meanwhile, a wafer 303 is held on top of a wafer stage 305 by vacuumabsorption, and the wafer stage 305 is disposed on a wafer base 307 viathree support legs 331A-331C, which can freely extend and retract withina specified range in the Z direction. The extending or retracting amountof the support legs 331A-331C is controlled by a support leg controller363 (see FIG. 26). By making the extending or retracting amount of thesupport legs 331A-331C the same, the position of the Z direction of thewafer 303 (focus position) is controlled. Controlling of the tilt angle(leveling) of the surface of the wafer 303 can be performed bycontrolling the extending or retracting amount of the support legs331A-331C independently.

The wafer stage 305 can continuously move on the wafer base 307 in the Xand Y directions by, for example, a linear motor method. Additionally,stepping can also be performed by the continuous movement. Furthermore,in order to perform coordinate measurement of the wafer 303 (wafer stage305), an X-axis moving mirror 344X (see FIG. 13) with a reflectingsurface that is substantially perpendicular to the X-axis and a Y-axismoving mirror 344Y (see FIG. 13) with a reflecting surface that issubstantially perpendicular to the Y-axis are fixed to a side surface ofthe wafer stage 305. Corresponding to these moving mirrors, an X-axisreference mirror 314 and a Y-axis reference mirror 313 are fixed to aside surface of the projection optical system 302.

During scanning exposure, the reticle stage 304 is moved at constantvelocity in the X-axis direction and, in synchronization with thismovement, the wafer stage 305 on which the wafer 303 is disposed ismoved in the opposite direction at a speed that is reduced by theprojection magnification β of the moving speed of the reticle stage 304,and scanning exposure is performed. After completion of the scanningexposure, the wafer stage 305 step-moves in the scanning direction or inthe Y-axis direction that is perpendicular to the scanning direction.The reticle stage 304 and the wafer stage 305 are moved insychronization in a direction opposite to the previous direction, andscanning exposure is performed. Hereafter, a pattern image of thereticle 301 is transferred to all the shooting areas on the wafer 303 bythe same operation.

Next, the reticle stage and the reticle base of the exposure apparatusof this example are explained. The reticle stage 304 is a guidelessstage which is disclosed in Japanese Laid-Open Patent Publication No.8-63231 (corresponding to parent application Ser. No. 08/698,827) andcan be driven in rotational directions about the optical axis AX of theprojection optical system 302 and about the X- and the Y-axes.Furthermore, a pair of linear motors that drive the reticle stage 304using a coil, which are fixed to a side surface of the reticle stage304, and a pair of motor magnets 311A and 311B, which are fixed to thetop of the reticle base 309 are provided, and the reticle base 309 issupported through a fluid-bearing (not depicted) such as an air bearingwith respect to a top surface 310 of a structural body 306. Ends of coilunits 312A and 312B disposed on the top of the structural body 306 areinserted from ends of the motor magnets 311A and 311B, and by the pairof linear motors structured by the motor magnets 311A and 311B and thecoil units 312A and 312B, the reticle base 309 is positioned in theX-axis direction with respect to the structural body 306. Furthermore,the structural body 306 is supported on the floor by vibration controlpads 349 through four legs 306 a, decreasing the vibration from thefloor.

When the reticle stage 304 moves during the scanning exposure, when thedriving reaction added by the motor magnets 311A and 311B is received,the reticle base 309 moves, so as to maintain a momentum in thedirection opposite to the moving direction of the reticle stage 304, bythe linear motor that has the coil units 312A and 312B. For example, ifthe masses of the reticle stage 304 and the reticle base 309 are 20 kgand 1000 kg, respectively, and the reticle base 309 thus has a mass 50times that of the reticle stage 304, if the reticle stage 304 moves byapproximately 300 mm during scanning, the reticle base 309 moves in thedirection opposite to the moving direction of the reticle stage 304 byapproximately 6 mm. By moving the reticle stage 304 and the reticle base309, so as to maintain the momentum, transmission of the drivingreaction to the structural body 306 of the reticle stage 304 can beprevented, and occurrence of vibration, which is a cause of disturbanceduring the positioning of the reticle stage 304, can be prevented.Furthermore, the displacement amount of the reticle base 309 isconstantly measured by a linear encoder (not depicted), and a currentsignal is formed when the reticle stage 304 is driven, based upon thismeasured value.

Furthermore, in the projection exposure apparatus of this example, thereis no movement of the center of the gravity of the system above thereticle base 309, so there is no fluctuation of the load to thestructural body 306 that supports the reticle base 309, and the positionof the reference mirrors 313 and 314 used for the measurement of therelative position between the reticle stage 304 and the projectionoptical system 302 does not fluctuate. Furthermore, when the reticlebase 309 is displaced a specified amount or more, if it mechanicallyinterferes with other members, it is acceptable to constantly maintainthe reticle base 309 at a substantially constant position whilecontrolling the coil units 312A and 312B, which are electromagneticdriving parts disposed between the reticle base 309 and the structuralbody 306, and decreasing the vibration transmitted to the structuralbody 306. By doing this, it is possible to prevent the reticle base 309from interfering with other members.

Next, a method of supporting the projection optical system of theexposure apparatus of this example is explained. FIG. 12 shows theprojection optical system 302 of the exposure apparatus of this example.In this figure, the point at which the object plane 315 and the imagesurface 316 are internally divided at the reduction projectionmagnification ratio β (=a/b) on the optical axis AX is defined as areference point 317 of the projection optical system 302. This referencepoint 317 is defined as a center, and even if the projection opticalsystem 302 is minutely rotated about an arbitrary axis within a planethat is orthogonal to the optical axis AX, the position relationshipbetween the object plane 315 and the image surface 316 does not change.The centers of the reference mirrors 313 and 314 are set on a planeperpendicular to the optical axis AX which pass through this referencepoint 317, and a laser beam is irradiated to these centers. Accordingly,when the projection optical system 302 is slid by a disturbancevibration, the reference point 317 also moves. Furthermore, the relativedisplacement between the reticle stage 304 and the wafer stage 305 andthe crossing point (reference mirrors 313 and 314) of the planeperpendicular to the optical axis AX of the projection optical system302 and the external surface of the lens barrel surrounding theprojection optical system 302 are constantly measured by the laserinterferometers 318X and 318Y. By controlling the reticle stage 304 andthe wafer stage 305 so as to match the measured value with a desiredvalue, it is possible to prevent position shifting of a pattern to beformed on the wafer 302.

Furthermore, the bottom part of the projection optical system 302 passesthrough an opening of a support plate 306 b which is disposed betweenthe legs 306 a, and is spaced from the opening by a gap. Additionally,the support part of the projection optical system 302 is formed by threeflexible rods 319A-319C extending from the structural body 306. Theextended lines of the respective rods 319A-319C cross at one point,which coincides with the reference point 317. Accordingly, even if theprojection optical system 302 is slid by receiving a disturbancevibration, the projection optical system 302 is minutely rotated usingthe center of the reference point 317 as a center of rotation, so theposition in the X and Y directions of the reference mirrors 313 and 314hardly changes. Furthermore, because the rods 319A-319C are flexiblystructured, high frequency vibrations dissipate, and hardly anydeterioration of the contrast occurs during transfer of the pattern.

Next, the wafer stage of the exposure apparatus of this example isexplained.

As shown in FIG. 11, the wafer stage 305 is positioned on top of thewafer base 307, and the wafer base 307 is supported by an elevatordriving part 308 that can displace several hundred μm in the verticaldirection. Between the wafer base 307 and the elevator driving part 308,a visco-elastic body (not depicted) is provided, and vibration from thefloor can be decreased. In addition, on the wafer base 307, five speedsensors (two of the five speed sensors, 336A and 336B, are shown in FIG.26) are provided, and the movement of the wafer stage 305 can bemeasured. It is also acceptable to use acceleration sensors instead ofspeed sensors.

FIGS. 13A-13D show the wafer stage 305 of the exposure apparatus of thisexample by enlargement. FIG. 13A is a plan view of the wafer table 320.FIG. 13B is a cross-sectional view of FIG. 13A along line B-B. FIG. 13Cis a front view (however, a carrier 321 is not depicted) of FIG. 13A.FIG. 13D is a cross-sectional view of FIG. 13A along line D-D. First, inFIG. 13D, the wafer stage 305 has a wafer table 320 on which a wafer 303is disposed and a carrier 321 that carries a driving/guiding part of thewafer table 320. The carrier 321 is movable on the wafer base 307 andcan be driven in the X and Y directions by a pulse motor type of planarmotor (for example, a Sawyer motor). In this example, when the carrier321 is driven, a pulse motor (not depicted) is used to supply pulsesaccording to the distance to a desired position by the open loop method.Because the pulses to a desired position is output to a motorcontroller, it is not necessary to provide a new position measurementdevice for the carrier 321. Furthermore, it is also acceptable to use anultrasonic wave motor as a flat motor.

Meanwhile, as shown in FIG. 13A, on the top surface of the wafer table320, a plurality of parallel shallow grooves 339 are disposed to vacuumabsorb the wafer 303. Many holes in the shallow grooves 339 are incommunication with a vacuum pump, which is not depicted. Furthermore,deep grooves 338 to receive the wafer carrier arms, described later, aredisposed in spaces between four shallow grooves 339 without interferingwith the shallow grooves 339. When a wafer 303 is fixed on the wafertable 320, the wafer carrier arm used as the carrier of the wafer 303can be taken in and out without interfering with the wafer table 320.

Furthermore, as shown in FIG. 13B, a guide shaft 322B is disposed in thescanning direction (X direction) via a support member 322C on thecarrier 321. A guide member 322A is fixed to the bottom surface of thewafer table 320, with the guide shaft 322B passing therethrough. Thewafer table 320 is restricted by a non-contact guide (for example, afluid bearing or a magnetic bearing) comprising the guide member 322A,which guides the wafer table 320 on the carrier 321 in the X direction,and the guide shaft 322B. Furthermore, in FIG. 13D, a pair of linearmotors 323A, 324A, and 323B, 324B are structured by coils 323A and 323Bfixed to the carrier 321 and magnets 324A and 324B fixed to the bottomsurface of the wafer table 320. The wafer table 320 is driven in the Ydirection and the rotational direction by the linear motors 323A, 324A,and 323B, 324B, which serve as non-contact electromagnetic drivingparts. The displacement of the wafer table 320 with respect to thecarrier 321 is measured by a linear encoder (not depicted), which servesas a non-contact position measurement device. Furthermore, the guideshaft 322B is structured so as to be rotatable about the guide axis by arotation member 322D. Additionally, when the linear motors 323A, 324Aand 323B, 324B generate a driving force in the same direction, the wafertable 320 moves in the guide axis direction (X direction). Conversely,when the linear motors 323A, 324A, and 323B, 324B generate a drivingforce in different directions, respectively, the wafer table 320 isrotated about the center of gravity.

The center of the thrust of the linear motors 323A, 324A, and 323B, 324Band the center of the guide member 322A are disposed so that they can bepositioned in a plane parallel to the top surface of the wafer base 307,and includes the center of gravity of the wafer table 320. Therefore,unnecessary inclination of the wafer table does not occur at the time ofacceleration of the wafer table 320. Furthermore, the size of the guideshaft 22B and the linear motors 323A, 324A, and 323B, 324B, only needsto be long enough for the movement of the wafer during the scanningexposure. Therefore, the size can be small so as to store the carrier321 below the wafer table 320, and the wafer can be moved at high speedwith high accuracy.

Furthermore, because the positioning accuracy needed for receiving thewafer 303 is approximately several μm, measurement by a laserinterferometer is not particularly needed in the area that receives thewafer 303, and the resolution of the pulse motor and/or the resolutionof the position measurement device of the carrier 321 is sufficient.Therefore, the moving mirrors 344X and 344Y which are provided for thewafer table 320 of FIG. 13 for the laser interferometers 318X and 318Ydo not necessarily have to cover the entire moving area of the wafertable 320. Only the length of the area in which precise positioning innm units is needed, that is, the length of the diameter of the wafer303, is needed.

The moving mirrors 344X and 344Y for the laser interferometer 318 aredisposed on side surfaces of the wafer table 320 of this example, andthe rotational angle about the Z-axis and the position of the wafertable 320 are measured. Side surfaces of the wafer table 320 are used asmoving mirrors 344X and 344Y for the laser interferometers 318X and318Y, so the wafer table 320 is of a size that substantiallycircumscribes the wafer 303, and it is extremely small and light,compared to a conventional wafer table. Furthermore, when the wafertable 320 is structured so as to dispose a rib structure in the bottomsurface with a thickness of approximately 3 mm by using a siliconcarbide, the weight of the wafer table 320 is approximately 5 kg.

FIG. 14 is a block diagram showing a structure of a controller thatcontrols both the wafer table 320 and the carrier 321. In FIG. 14, themain controller 350 supplies desired positions of the carrier 321 andthe wafer table 320, respectively, to subtractors 354 and 357 within thewafer stage controller 325. Furthermore, the relative displacementamount of the wafer table 320 with respect to the carrier 321 isdetected by a hypothetical subtractor 356 and a displacement sensor(linear encoder) 360. A table controller 355 drives the wafer table 320,based upon the output of the subtractor 354 and the displacement sensor360, and the carrier controller 358 drives the carrier 321 based uponthe output of the subtractor 357. The subtractor 354 outputs a valuecorresponding to the measured value of the laser interferometers 318Xand 318Y subtracted from the desired value, and the subtractor 357outputs a value that corresponds to the measured value of a hypotheticallinear encoder 359 for the carrier 321 subtracted from the desiredvalue.

When the laser interferometers 318X and 318Y (see FIG. 11) are not usedwhile the mode switch 326 is OFF, that is, in the case of theapproximate positioning, based upon the signal from the displacementsensor 360 that serves as a linear encoder, the wafer stage controller325 controls the linear motors 323A, 324A and 323B, 324B of FIGS.13A-13D so as to constantly position the wafer table 320 at the middlepoint of the moving range with respect to the carrier 321. Furthermore,when the driving part of the carrier 321 has an encoder 359, the carriercontroller 358 moves the carrier 321 to a desired position withreference to the encoder 359. When an encoder is not especiallyprovided, such as in the case of a pulse motor in this example, pulsesto a desired position are output to the motor controller and the carrier321 is controlled. Therefore, regardless of the existence of an encoder,the wafer table 320 is controlled so as to be moved while following themovement of carrier 321.

When the mode switch 326 of FIG. 14 is in the ON state and the wafertable 320 moves based upon the measured value of the laserinterferometers 318X and 318Y, that is, in the case of precisepositioning, based upon the output of the subtractor 354, whichreferences the measured value of the laser interferometers 318X and318Y, the table controller 355 causes the linear motors 323A, 324A and323B, 324B to generate thrust with respect to the wafer table 320, andcauses the wafer table 320 to move. Furthermore, the carrier 321 iscontrolled just like in the approximate positioning.

When the wafer table 320 moves at constant velocity while using thelaser interferometers 318X and 318Y, that is, at the time of scanningexposure, the table controller 355 causes the linear motors 323A, 324Aand 323B, 324B to generate thrust and move the wafer table 320 whilereferring to the output of the subtractor 354, which has subtracted themeasured value of the laser interferometers 318X and 318Y. At this time,the carrier 321 maintains a still state, and only the wafer table 320moves at a constant velocity. Therefore, it is only the light weightwafer table 320 that generates the driving reaction with respect to thewafer base 307 during the scanning exposure, so the disturbance reactionto be generated becomes extremely small, and scanning exposure can beperformed at high speed with high accuracy.

Next, the guide member 322A and the guide shaft 322B of the wafer table320 of the exposure apparatus of this example are explained.

FIG. 15A-C show the guide member 322A and the guide shaft 322B of FIGS.13A-D by enlargement. In this figure, springs 327A and 327B are providedas elastic bodies at both ends of the guide shaft 322B. When the wafertable 320 reciprocates with respect to the carrier 321, first, as shownin FIG. 15A, kinetic energy of the wafer table 320 is converted topotential energy via the guide member 322A and is stored in the spring327A. Next, as shown in FIG. 15B, the potential energy that has beenstored in the spring 327A is again converted to kinetic energy of thewafer table 320, and the wafer stage controller 325 of FIG. 11 controlsthe wafer table 320 using the kinetic energy so that it moves the wafertable 320 at the speed of −V. Furthermore, as shown in FIG. 15C, whenthe support member 322A contacts the spring 327B, an opposing force of+F occurs in the spring 327B and the kinetic energy of the wafer table320 is again converted to potential energy and is saved in the spring327B. Therefore, mechanical energy to be consumed in the case ofreciprocation of the wafer table 320 is mainly only the heat from theviscosity resistance of the wafer table 320 with respect to the air, andfrom when the elastic bodies are deformed. Thus, the heating amount ofthe linear motors 323A, 324A, and 323B, 324B becomes extremely small.

FIG. 16A shows a speed curve of the wafer table 320 when the movingspeed of the wafer table 320 is shifted to a constant speed (0.5 m/s)and is moved on the guide shaft 322B, which is hypothetically defined asa guide axis without an elastic body. In FIG. 16A, the horizontal axisshows time t (s), and the vertical axis shows the moving speed V (m/s)of the wafer table 320. Furthermore, FIG. 16B shows the thrust of thelinear motors 323A, 324A and 323B, 324B at that time. In FIG. 16B, thehorizontal axis is time t (s), and the vertical axis is a thrust F(N) ofthe linear motors. Furthermore, the mass of the wafer table 320 which isused is 5 kg. FIG. 17A corresponds to FIG. 16A and shows a speed curveof the wafer table 320 calculated assuming the case where an ideal wafertable 320 without vibration is accelerated to a certain speed on theguide axis provided with a specified spring. FIG. 17B shows a thrustF(N) of the linear motors 323A, 324A and 323B, 324B, which is calculatedassuming the case where a wafer table 320 that resonates is controlledwith the speed curve of FIG. 17A as the speed governing value. WhenFIGS. 16A-B are compared with FIGS. 17A-B, the ratio of the heatingamount of the linear motors 323A, 324A, and 323B, 324B is 1:0.94, whichis substantially the same.

FIG. 18A shows a speed curve when the speed curve of FIG. 17A is thespeed governing value, the guide shaft 322B provided with the springs327A and 327B of FIG. 15 is used, and the wafer table 320 is acceleratedto a constant speed. FIG. 18B shows the thrust of the wafer table 320and thrust generated by the linear motors 323A, 324A and 323B, 324B. InFIG. 18B, the horizontal axis is time t (s), and the vertical axis isthrust F(N). The curve A in a solid line is the thrust added to thewafer table 320, and the curve B in the single-dot chain line shows thethrust of the linear motors 323A and 323B. The spring constant of thesprings 327A and 327B is 1,000 N/m, and this is 40% of an ideal springconstant (2,500 N/m). By using the springs 327A and 327B, the heatingamount of the linear motors 323A, 324A and 323B, 324B can be reduced toapproximately 35% of the heating amount of the case when an elastic bodyis not used.

FIG. 19A shows a speed curve when the wafer table 320 is accelerated toa constant speed using a guide shaft 322B with springs 327A and 327Bwith the optimum spring constant value of 2,500 N/m. FIG. 19B shows thethrust F of the wafer table 320 at that time. The heating amount of thelinear motors 323A, 324A and 323B, 324B can be reduced to 1% or less ofthe case when an elastic body is not used. Thus, by having the springs327A and 327B at both ends of the guide shaft 322B, the heating amountof the linear motors 323A, 324A and 323B, 324B can be reduced when thewafer table 320 constantly moves.

However, in the case of the still-positioning of the wafer table 320′ atthe end of the guide shaft 322B, the linear motors 323A, 324A and 323B,324B need to generate a thrust that can be balanced with the resistanceof the springs 327A and 327B, which causes the heating amount of thelinear motors 323A, 324A and 323B, 324B to increase.

FIG. 20 shows the resistance of the springs 327A and 327B at the end ofthe guide shaft 322B provided with the springs 327A and 327B. In FIG.20, the horizontal axis shows distance D(m) from the end of the guideshaft 322B, and the vertical axis shows the resistance F_(P)(N) of thesprings 327A and 327B. In order to still-position the wafer table 320 atthe end of the guide shaft 322B, the linear motors 323A, 324A and 323B,324B need to generate a thrust (50 N) that is large enough to balancethe resistance of the springs 327A and 327B. Otherwise, the heatingamount increases. Therefore, in this case, a magnetic member is fixed tothe end of the guide shaft 322B. Preferably, the heating amount isreduced when the wafer table 320 is still-positioned by using theattractive force of the magnet member.

FIGS. 21A-C show the guide member 322A and the guide shaft 322B to whichthe magnetic member is fixed, corresponding to FIGS. 15A-C. In FIGS.21A-C, steel plates 329 are fixed to both ends of the guide member 322A,and magnets 330 are fixed at both ends of the guide shaft 322B. As shownin FIGS. 21A-C, when the wafer table 320 is still-positioned at the endof the guide shaft 322B via the guide member 322A, by using theattraction of the steel plate 329 and the magnet 330, the thrust of thelinear motors 323A, 324A and 323B, 324B needed against the resistance ofthe springs 327A and 327B can be reduced and the heating amount can becontrolled. Furthermore, in the case of moving the wafer table 320 at aconstant velocity, as shown in FIG. 21B, by using the resistance of thesprings 327A and 327B, the heating amount of the linear motors 323A,324A, and 323B, 324B is reduced. In this case, the heating amount of thelinear motors can be reduced to approximately ⅙ of the case when aspring or the like is not used on the guide shaft 322B. Additionally,when there is no limitation to the thrust of the linear motors, thepotential energy at both ends of the guide shaft 322B can be set at 0.Furthermore, the setting relationship between the steel plates 329 andthe magnets 330 can be reversed, and it is acceptable to disposeanything that generates attractive force opposing the resistance of theelastic member of the springs 327A and 327B or the like at the ends ofthe guide shaft 322B.

FIG. 22A shows a speed curve that is calculated assuming the case wherean ideal wafer table 320 without vibration is accelerated to a constantspeed on a guide shaft 322B provided with springs, steel plates, andmagnets. In FIG. 22A, the horizontal axis is time t(s), and the verticalaxis is moving speed V(m/s) of the wafer table 320. FIG. 22B shows athrust of the linear motors 323A, 324A and 323B, 324B calculatedassuming the case where the wafer table 320 that resonates is controlledwith the speed curve of FIG. 22A as the speed governing value. In FIG.22B, the horizontal axis is time t(s), and the vertical axis is thrustF(N) of the linear motors. FIG. 23A shows a speed curve when the speedcurve of FIG. 22A is the speed governing value and the wafer table 320is accelerated to a constant speed on the guide axis 322 provided withthe steel plates 329 and the magnets 330. FIG. 23B shows the thrust F(curve A in solid line) that is added to the wafer table 320 at thattime, and the thrust F (curve B in single-dot chain line) of the linearmotors 323A, 324A and 323B, 324B. The spring constant of the springs327A and 327B is 2,000 N/m, which is the optimum spring constant. Theheating amount of the linear motors 323A, 324A and 323B, 324B in thiscase is 1% or less of the case when springs, magnets, and steel platesare not used. Furthermore, compared to the case where a magnet or thelike is not provided, the thrust required at the start of moving issmall and the wafer table 320 is gradually accelerated, so there is anadvantage such that the mechanical resonance of the wafer table 320 canbe eased.

FIG. 24 shows the resultant force F_(P)(N) between the resistance of thesprings 327A and 327B and the attraction between the magnet 330 and thesteel plate 329 at an end of the guide shaft 322B to which the steelplate 329 and the magnet 330 are fixed according to FIG. 20. In FIG. 24,the horizontal axis is distance D(m) from the end of the guide shaft322B. As the magnet 330 is fixed to the end of the guide shaft 322B, andthe steel plate 329 is fixed to the guide member 322A, the thrust of thelinear motors 323A, 324A and 323B, 324B required for thestill-positioning of the wafer table 320 at the end of the guide shaft322B can be reduced and the heating amount can be controlled.

Next, the structure of the support legs 331A-331C that support the wafertable 320 with respect to the wafer base 307 of the exposure apparatusof this example is explained.

FIG. 25A is an enlarged view showing the support leg 331A and the likeof the wafer table 320. FIG. 25B is a side view. In the support leg331A, between slot 331Aa and a lower slot 331Ab is a displacement part334. A fluid bearing 332A is attached to the bottom of the displacementpart 334 through a spherical bearing 335 so that it can be rotated. Inthe same manner, as shown in FIG. 13, fluid bearings 332B and 332C arefixed to the other support legs 331B and 331C. The fluid bearing 332A isdisposed on the wafer base 307 of FIG. 13 by a hydrostatic pressurefluid bearing method. Additionally, as shown by the support leg 331B ofFIG. 13C, piezoactuators 333 are fixed to the support legs 331A-331C,and the piezoactuators 333 are fixed to the wafer table 320 via fixingmembers 353.

Referring to FIGS. 25A-B, a displacement enlargement mechanism that canbe extended and retracted in the direction of support is structured bythe piezoactuator 333 and the displacement part 334. The fluid bearing332A has a magnet or a vacuum absorption part for applying pressure. Ingeneral, because the displacement by the piezoactuator is onlyapproximately 60 μm, a displacement enlargement mechanism is needed. Thedisplacement enlargement mechanism of this example uses a parallelmotion link. When the extending/retracting part of the piezoactuator 333presses an input point A of the slot 331Aa of the support leg 331A, theinput point A is linearly displaced in the horizontal direction by aminute displacement area. Then, point B of the link mechanism part ofthe displacement part 334 of the displacement enlargement mechanism isrotated about center point C, and point D is displaced in a verticaldirection as a result thereof. In the displacement part 334 of thedisplacement enlargement mechanism of this example, the slope of thelink is 26.6°, the displacement enlargement percentage becomes double,and it can be displaced to a maximum of 120 μm. Furthermore, byadjusting the displacement of the displacement part 334 of the supportlegs 331A-331C, correction of the tilt angle (leveling) of the wafertable 320 and the correction of the position in the vertical direction(focus adjustment) with respect to the wafer base 307 are performed.

Furthermore, even if the support legs 331A-331C are displaced 120 μM,which is the maximum displacement amount, if focus adjustment andleveling cannot be appropriately performed, the front surfacepositioning of the wafer 303 is premeasured before the exposure starts,and the elevator driving part 308 of FIG. 11 is driven and the waferbase 307 is positioned so that the position of the surface of the wafer303 can be placed at a specified position (the image plane of theprojection optical system 302). After that, focus adjustment andleveling are performed by adjusting the support legs 331A-331C.

FIG. 26 is a block diagram showing a structure of a controller thatcontrols the reticle stage 304 and the wafer stage 305. In FIG. 26, themain controller 350 supplies the desired value of the displacementamount to a desired position in the X and Y directions of the wafertable 320 of the wafer stage 305 and the Z direction of the support legs331A-331C to the subtractors 361 and 362, respectively. Based upon thevalue corresponding to a value that is multiplied by −¼ of the measuredvalue, from the desired position in the subtractor 361 of the laserinterferometers 318X and 318Y in the converter 365, the wafer stagecontroller 325 drives the wafer stage 305. The subtractor 362 adds avalue obtained by integrating the speed in the Z direction of the waferbase 307, which is measured by the speed sensor 336B, to the desiredvalue, and further supplies a value obtained by subtracting a defocusamount of the wafer stage 305, which is measured by an autofocus sensor,not depicted, to a support leg controller 363. The support legcontroller 363 controls the extending or retracting amount of thesupport legs 331A-331C, which support the wafer stage 305 based upon thesupplied value, and focus adjustment and leveling can be performed.Furthermore, the reticle stage controller 352 controls the reticle stage304, based upon the detection result of the vibration component (yawing)of the projection optical system 302 in the rotational direction aboutthe optical-axis and the displacement of the wafer base 307 in thedirection perpendicular to the scanning direction detected by the speedsensor 336A, and on the value corresponding to the measured value of thelaser interferometers 318X and 318Y subtracted from the output of theconverter 365 using the subtractor 366. Thus, the effects of vibrationof the wafer base 307 in the horizontal direction can be reduced.Furthermore, the vibration of the wafer base 307 in the Z direction canbe reduced by a visco-elastic body 364.

Next, the wafer carrier mechanism of the exposure apparatus of thisexample is explained. In FIG. 11, in front of the wafer base 307, acarrier base 345 is disposed via a vibration control table 351. A wafercarrier mechanism such as wafer carrier arms 340A and 340B and the wafercassette 348 and/or the like are disposed on the carrier base 345.

FIG. 27A is a plan view showing part of the wafer carrier mechanism ofthe exposure apparatus of this example. FIG. 27B is a side view. First,the wafer stage 305 on which is disposed a wafer 303A to which exposurehas been completed moves from the exposure completion position A to thewafer carrier position B, and the wafer 303A moves to the position P1.At this time, three fingers of the wafer carrier arms 340A are insertedinto spaces which are surrounded by the wafer 303A and the deep grooves338 of the wafer table 320, and do not contact the wafer table 320. Thewafer carrier arm 340A is attached on the support part 367A via anactuator 369A that can be extended and retracted in the Z direction andthat can be rotated, and the support part 367A moves on the carrier base345 by a driving part 368A. A support part 367B, an actuator 369B, and adriving part (not depicted) are provided on another wafer carrier arm340B as well. When the wafer stage 305 is still, the wafer table 320releases the fixation of the wafer 303A by vacuum absorption, and thewafer carrier arm 340A vacuum-absorbs the wafer 303A and is raised bythe actuator 369A. Furthermore, a wafer 303A to which exposure has beencompleted is collected to the wafer cassette 348 shown in FIGS. 28A-B.

When the wafer carrier arm 340A raises, the wafer stage 305simultaneously moves at high speed to below the wafer carrier arm 340B(wafer carry-in position C) which holds a non-exposed wafer 303B. Whenthe wafer table 320 of the wafer stage stops, the wafer carrier arm 340Bis lowered by the actuator 369B, and the non-exposed wafer 303B isdisposed on the wafer table 320 and is vacuum-absorbed. At this time,because the wafer carrier arm 340B is also inserted into the deepgrooves 338, it does not contact the wafer table 320. After this, thewafer stage 305 moves at high speed from the wafer carrier-in position Cto the exposure start position D, the wafer 303B moves to the positionP2, and exposure begins. At the same time, the wafer carrier arm 340Btakes a new wafer out from the wafer cassette 348 of FIGS. 28A-B andwaits.

When superposition exposure is performed, the rotational angle of thewafer of the exposure object is measured in advance and the wafer table320 is rotated during the positioning so as to cancel the angle of thewafer stage 305 at the wafer carrier position C. By doing this, when thewafer table 320 is facing in the scanning direction, a pattern that isformed in a shooting area that is already arrayed in a grid state on thewafer and a pattern image of the reticle 301 can be in a specifiedpositional relationship.

FIG. 28A is a plan view showing the vicinity of the wafer cassette 348when a wafer is carried out. FIG. 28B is a side view of FIG. 28A. Thewafer carrier arms 340A and 340B can be freely driven in threedirections such as a rotational direction about the Z-axis, a scanningdirection (X direction), and a vertical direction (Z direction). A wafercassette support member 347 that supports the wafer cassette 348 on thecarrier base 345 can be freely driven in the vertical direction. When analready-exposed wafer 303A is collected to the wafer cassette 348,first, the wafer carrier arm 340A that holds the wafer 303A is revolvedby the actuator 369A. At the moment the wafer 303A goes through theposition P4 and reaches the front surface of the wafer cassette 348, thesupport member 367A of the wafer carrier arm 340A linearly moves to theposition P3 in the X-axis direction and the wafer carrier arm 340A isrevolved at the same time so that the wafer 303A linearly moves in theY-axis direction. Next, when the wafer 303A reaches a predeterminedposition within the wafer cassette 348, vacuum absorption by the wafercarrier arm 340A is released, and the wafer cassette support member 347raises and lifts up the wafer 303A. Then, the wafer carrier arm 340Aperforms an opposite operation compared to the previous process andwithdraws.

FIG. 29A is a plan view showing the vicinity of the wafer cassette 348when the wafer is carried in. FIG. 29B is a side view of FIG. 29A. Whenthe wafer is carried out from the wafer cassette 348, first the wafercarrier arm 340B moves below the non-exposed wafer 303B. When the wafercarrier arm 340B stops, the wafer cassette support member 347 lowers,and the wafer 303B is disposed on the wafer carrier arm 340B. Then,after the wafer carrier arm 340B vacuum-absorbs the wafer 303B, thesupport member 367B of the wafer carrier arm 340B linearly moves in theX-axis direction, the wafer carrier arm 340B is revolved by the actuator369B and takes the wafer 303B out from the wafer cassette 348. It thenwaits until the wafer stage 305 arrives. Furthermore, the wafer carrierarm 340B can linearly move parallel to the front surface of the device,so it is also possible to structure the device in-line with surroundingdevices such as a coater or a developer.

Thus, as the wafer stage 305 of FIG. 27 moves to the position ofcarrying out the wafer or the position of carrying in the wafer, it isnot necessary to temporarily fix and support the wafer as in aconventional exposure apparatus, and there is no need for receiving andgiving the wafer between wafer carrier arms. Therefore, the probabilityof foreign objects attaching to the wafer and the probability of carriererror can be reduced. Furthermore, a larger mass wafer can be carriedand a larger size of wafer can be developed, compared to when the waferis carried to the exposure position by wafer carrier arms, because theeffects of vibration of the wafer carrier arms are not easily receiveddue to the mass of the wafer.

While the present invention has been described with reference topreferred embodiments thereof, it is to be understood that the inventionis not limited to the disclosed embodiments or constructions. To thecontrary, the invention is intended to cover various modifications andequivalent arrangements. In addition, while the various elements of thedisclosed invention are shown in various combinations andconfigurations, which are exemplary, other combinations andconfigurations, including more, less or only a single element, are alsowithin the spirit and scope of the invention.

1. A projection optical device comprising: a projection optical systemthat projects an energy beam; and a support device having a flexiblestructure to support the projection optical system.
 2. The projectionoptical device of claim 1, wherein the flexible structure comprises arod member.
 3. The projection optical device of claim 2, wherein the rodmember includes three rods.
 4. The projection optical device of claim 3,wherein extended lines of the respective rods cross at a reference pointof the projection optical system.
 5. The projection optical device ofclaim 1, wherein the support device supports the projection opticalsystem from an upper side of the projection optical system.
 6. Theprojection optical device of claim 1, wherein the support devicecomprises a vibration isolation member that decreases vibration from thefloor.
 7. The projection optical device of claim 1, wherein the supportdevice supports an outer portion of the projection optical system by theflexible structure.
 8. An exposure apparatus that irradiates an energybeam to a substrate, the exposure apparatus comprising: a projectionoptical system that projects the energy beam to the substrate; and asupport device having a flexible structure to support the projectionoptical system.
 9. The exposure apparatus of claim 8, wherein theflexible structure comprises a rod member.
 10. The exposure apparatus ofclaim 9, wherein the rod member includes three rods.
 11. The exposureapparatus of claim 10, wherein extended lines of the respective rodscross at a reference point of the projection optical system.
 12. Theexposure apparatus of claim 8, wherein the support device supports theprojection optical system from an upper side of the projection opticalsystem.
 13. The exposure apparatus of claim 8, wherein the supportdevice comprises a vibration isolation member that decreases vibrationfrom the floor.
 14. The exposure apparatus of claim 8, wherein thesupport device supports an outer portion of the projection opticalsystem by the flexible structure.
 15. The exposure apparatus of claim 8,further comprising a substrate stage that holds the substrate, thesubstrate stage being separated from the support device.
 16. Theexposure apparatus of claim 8, further comprising: a mask stage locatedabove the projection optical system to hold a mask having a pattern, theprojection optical system projecting a patterned energy beam to thesubstrate; and a counter-mass that moves to cancel a reaction force thatis generated by movement of the mask stage.
 17. The exposure apparatusof claim 16, further comprising a substrate stage that holds thesubstrate, the substrate stage being separated from the support device.18. A projection method, comprising: providing a projection opticalsystem that projects an energy beam; and supporting the projectionoptical system by a flexible structure.
 19. The method of claim 18,wherein the flexible structure comprises a rod member.
 20. The method ofclaim 19, wherein the rod member includes three rods.
 21. The method ofclaim 20, wherein extended lines of the respective rods cross at areference point of the projection optical system.
 22. The method ofclaim 18, wherein the flexible structure supports the projection opticalsystem from an upper side of the projection optical system.
 23. Themethod of claim 18, further comprising decreasing vibration from thefloor by a vibration isolation member.
 24. The method of claim 18,wherein the flexible structure supports an outer portion of theprojection optical system.
 25. An exposure method that irradiates anenergy beam to a substrate, the method comprising: projecting the energybeam to the substrate by a projection optical system; and supporting theprojection optical system by a flexible structure.
 26. The method ofclaim 25, wherein the flexible structure comprises a rod member.
 27. Themethod of claim 26, wherein the rod member includes three rods.
 28. Themethod of claim 27, wherein extended lines of the respective rods crossat a reference point of the projection optical system.
 29. The method ofclaim 25, wherein the flexible structure supports the projection opticalsystem from an upper side of the projection optical system.
 30. Themethod of claim 25, further comprising decreasing vibration from thefloor by a vibration isolation member.
 31. The method of claim 25,wherein the flexible structure supports an outer portion of theprojection optical system.
 32. The method of claim 25, furthercomprising supporting the substrate by a substrate stage that isseparated from the projection optical system.
 33. The method of claim25, further comprising: providing a mask that has a pattern to a maskstage located above the projection optical system, the projectionoptical system projecting a patterned energy beam to the substrate; andmoving a counter-mass to cancel a reaction force that is generated bymovement of the mask stage.
 34. The method of claim 33, furthercomprising supporting the substrate by a substrate stage that isseparated from the projection optical system.